This invention relates to a device for determining engagement of a lockup clutch, particularly to a device for determining engagement of a lockup clutch in a system for integrally controlling an automatic transmission and an engine, wherein gear stages can be automatically switched in accordance with a present shift map, the lockup clutch of a torque converter can be engaged on at least one gear stage, and the engine torque is changed during shifting to maintain satisfactory shift characteristics.
Automatic transmissions comprising gear transmission mechanisms, a plurality of frictionally engaging devices, and hydraulic pressure control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved in accordance with a preset shift map, are well known in the transmission art.
Furthermore, in vehicle automatic transmissions of the type described, various systems for integrally controlling an automatic transmission and an engine, wherein engine torque is changed during shifting to obtain satisfactory shift characteristics and durability of the frictionally engaging devices have been used (For example, Japanese Patent Laid-Open No. 69738/1980). More specifically, systems of this type change that the amount of torque transmitted from the engine during shifting and control the amount of absorbed energy in various members in the automatic transmission or in the frictionally engaging devices for controlling these members to complete shifting within a short period of time with low shift shock. As a consequence, satisfactory shift feeling is given to a driver and durability of the frictionally engaging devices is improved.
Furthermore, motor vehicle automatic transmissions implementing a torque converter lock up clutch during part of all of the gear stages to improve the fuel consumption rate, are also well known in the transmission art.
Integral controls for automatic transmissions which have a lockup clutch and an engine previously have not determined how engine torque should change in accordance with engaged or non-engaged states of the lockup clutch. However, engine torque chang timing must be accurately performed. Movements of members of the automatic transmission are considerably different depending on either the engaged or non-engaged states of the lockup clutch. As a consequence, in determining the engine torque change timing, it is desirable to alter the method of determining the timing depending on the engaged or the non-engaged states of the lockup clutch.
For example, when the engine torque change timing is determined by use of a timer, the value of the timer should be changed depending on either the engaged or non-engaged states of the lockup clutch.
Furthermore, when the engine torque change timing is determined by the actual movements of members of the engine or the automatic transmission, it is desirable to change the method of determining such timing. Namely, in the case of an up-shifting from the non-engaged state of the lockup clutch, it is desirable to determine whether or not the engine rotary speed is lower than the precedingly measured value. Whereas, in the case of an up-shifting from the engaged state of the lockup clutch, it is desirable to determine whether or not the enging rotary speed is lower than a turbine rotary speed of the torque converter, which is obtained from the output shaft rotary speed and the gear ratio on the low gear side. According to the above-described methods, the engine torque change timing can be determined early and reliably.
However, in automatic transmission lockup mechanisms, in general, a lockup piston is engaged under oil pressure. Furthermore, engagement and disengagement are preformed by switching oil lines by ON-OFF operated electromagnetic valves in response to engaging signals from a microcomputer. As a consequence, there is some time delay between the engaging signal which is outputted from the microcomputer and the actual engagement. As a result, there occurs a timewise deviation between an engagement determination made in response to the engaging signal of the microcomputer and the actual engaged state of the lockup clutch.
More specifically, although the microcomputer determines that the lockup clutch is in the engaged state, there are instances where the lockup clutch is not actually engaged. When a shifting takes place in the above-described case, when the method of determining the engine torque change timing is differed depending on either the engaged or non-engaged states of the lockup clutch as aforesaid, determination of the timing for performing the engine torque change control cannot be performing properly. As a result, the torque change control is carried out at an unsuitable time.